<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <script>
      var mony = 100,
        oper = 0;
      var str = prompt("请输入您的操作：\n1.存钱\n2.取钱\n3.显示余额\n4.退出");
      var num = parseInt(str);
      switch (num) {
        case 1:
          oper = prompt("请输入您想存的数额") - 0;
          mony += oper;
          alert("您现在的余额为:" + mony);
          break;
        case 2:
          oper = prompt("请输入您想取的数额") - 0;
          mony -= oper;
          alert("您现在的余额为:" + mony);
          break;
        case 3:
          alert("您现在的余额为:" + mony);
          break;
        case 4:
          alert("您正在退出");
          break;
        default:
          break;
      }
    </script>
  </head>
  <body></body>
</html>
